“Plating” which is a technique for coating a surface of solid with metal is used for providing various functions to the surface, in addition to the traditional purpose such as providing decorative properties. For example, electrical properties (electrical conductivity, contact resistance, magnetic properties, shielding properties against electromagnetic wave, high frequency properties, etc.), mechanical properties (strength, rublicity, frictional characteristics, etc.), physical properties (solderability, bonding properties, adhesive properties, etc.), optical properties (optical reflection properties, light absorption characteristics, etc.), chemical properties (corrosionproof properties, bactericidal properties, chemical resistance, etc.), and thermal properties (heat resistance, thermal conductivity, etc.) and the like can be provided.
Therefore, the plating technique has a wide range of the filed where the technique may be active, and it is applied in various fields such as an ornament, circuit-boards, electric contacts, semiconductor parts, lead frames, connectors, copper foils, automobile parts, electric home appliances, chemical apparatuses, plastics, engines, clocks, eyeglasses, substrates for coating, parts for electronics industry, containers, insoluble anodes, parts for printing, rubber products, sliding components, bearings, tools, rolls, building components, steel products, magnetic recording device, heat absorbing components and the like. It is predicted that the field in which the plating technique may be applied will increase.
Among the plating technique, a method for forming a metal coating without externally providing electricity is an electroless plating method. The electroless plating, which is different from an electro-plate method in which electrodeposition occurs by applying a voltage, has an advantage that a metal coating may be formed not only on metals but also on insulants such as glass, plastics and ceramics etc. Further, the electroless plating also has characteristics that it is not necessary to consider the distribution of the electric current and voltage, no anode inserted into the plating bath is required, a deposited coating is homogeneous, the thickness of the coating may become thin, plating to fine parts may be performed. Utilizing these characteristics, the electroless plating is also applied in various fields as described above.
In the field of electronics which is one of the representative filed where the electroless plating is applied, electronic parts have been significantly miniaturized and highly integrated, and their shapes have been complicated, too. Therefore, a technique for the fine plating is required (a nano-technology of top-down type). On the other hand, in the industry, a technique for assembling and constructing supermicro-mechanism at the level of atoms and molecules which has been expected to lead to an epoch-making development of materials, electronics, information communication, environment, energy, biotechnology, creation of medicament, medical service and the like is gathering much interest (a nano-technology of bottom-up type). Such a tendency of science and technology has a potential of creating a novel functional material(s) using the fine plating technique.
Under the background as described above, until now, there have been several examples where electroless plating was applied to a fine organic compound.
For example, in Hong-xia Guo et. al., “Synthesis of Novel Magnetic Spheres by Electroless Nickel Coating of Polymer Spheres”, Surface & Coating Technology, Vol. 200, Elsevier B. V, 2005, p2531-2536, describes polymethylmethacrylate (PMMA) having a magnetic Ni plated layer on its surface by the electroless plating.
In this document, PMMA particles of about 1.9 μm are sensitized by adsorbing Sn2+ on the surface of the particles using SnCl2 solution, and then an oxidation-reduction reaction is caused by dipping the particles obtained into a hydrochloric acid solution of PdCl2, and then metal particles of Pd are formed as a catalytic portion on the surface of PMMA particles. The obtained particles are subjected to electroless plating of Ni to form final products having an average particle diameter of 2.07 μm.
Further, in Masaru Nakagawa, “Tubular and twisted Ni—P fibers molded from morphology-tunable and recyclable organic templates of hydrogen-bonded supramolecular assemblages”, Adv. Mater., Vol. 17, Wiley-VCH, 2005, p200-205, describes a hollow metal fiber wherein azopyridine carboxylic acid (APC) having propyl, methyl, sec-butyl or ethoxy group(s) is used as a template.
In this document, a fibrous molecular assemblage of APC bonded by a hydrogen bonding(s) (external diameter is about 100 nm-1 μm) is prepared. Subsequently, the fibrous molecular assemblage is soaked in an acidic aqueous solution containing PdCl2 as a precursor of catalyst and then an electroless plating of Ni—P alloy is performed. Further, the obtained material is dispersed in an alkaline aqueous solution for removing the internal organic template and thus the final product is obtained.